British Prime Minister Boris Johnson on Wednesday announced the tightening of virus restrictions in England as Omicron variant cases surge, including guidance to work from home and mandatory vaccine passports.

Johnson said at a briefing that as the rate of Omicron cases was doubling every two to three days, it was "the proportionate and the responsible thing to move to Plan B in England".

As part of a raft of measure, the government is reintroducing advice to work at home in England from Monday, the prime minister said.

He added that the government in a week's time will make it compulsory to show Covid vaccine passports in England for the first time, while the devolved administrations of Scotland and Wales have already brought in similar measures.

These will be required "for entry into nightclubs and venues where large crowds gather", Johnson said.

The government is also making it a legal requirement to wear masks in "most public indoor venues, including theatres and cinemas", he said.

Johnson said that it was becoming increasingly clear that the Omicron variant is spreading much quicker than the previously dominant Delta variant and "we can't yet assume Omicron is less severe than previous variants".

"We just have to respond today in the way that we are," he said, while insisting the new measures do not amount to a lockdown and people can continue with Christmas parties and children's events such as Nativity plays.

The prime minister stressed the importance of people taking up vaccines and the booster doses now being offered.

"The single biggest thing that every one of us can do is to get our jabs and crucially to get that booster as soon as our turn arrives," he said.